Motion compensating floor system and method

Abstract

A motion compensating system is usable on a vessel during well intervention operations through a riser. The system includes a first floor; a second floor; a plurality of hydraulic cylinders connecting the first floor to the second floor; a bearing retainer attachable to the second floor; a spherical bearing provided between the second floor and the bearing retainer, wherein the spherical bearing includes a central opening therethrough for the riser to allow angular movement of the riser relative to the first and second floors; an insert bearing sleeve at least partially located inside the central opening of the spherical bearing; and a slip bowl attachable to the insert bearing sleeve. Each of the first floor, the second floor, the bearing retainer, the insert bearing sleeve and the slip bowl have an opening therethrough for the riser, and each opening is aligned with the central opening of the spherical bearing.

The invention claimed is: 
     
       1. A motion compensating system usable on a vessel during well intervention operations through a riser, the motion compensation system comprising:
 a first floor; 
 a second floor; 
 a plurality of hydraulic cylinders connecting the first floor to the second floor; 
 a bearing retainer attachable to the second floor; 
 a spherical bearing provided between the second floor and the bearing retainer, wherein the spherical bearing includes a central opening therethrough for the riser to allow angular movement of the riser relative to the first floor and the second floor; 
 an insert bearing sleeve at least partially located inside the central opening of the spherical bearing; and 
 a slip bowl attachable to the insert bearing sleeve, 
 wherein each of the first floor, the second floor, the bearing retainer, the insert bearing sleeve and the slip bowl have an opening therethrough for the riser, and each opening is aligned with the central opening of the spherical bearing. 
 
     
     
       2. A motion compensating system according to  claim 1 , wherein each of the plurality of hydraulic cylinders is pivotally connected to the first floor and the second floor for moving the first floor with respect to the second floor. 
     
     
       3. A motion compensating system according to  claim 1 , wherein the plurality of hydraulic cylinders are connected to the first floor around the opening of the first floor, and connected to the second floor around the opening of the second floor. 
     
     
       4. A motion compensating system according to  claim 1 , wherein a total of three hydraulic cylinders connect the first floor to the second floor. 
     
     
       5. A motion compensating system according to  claim 1 , wherein the first floor is configured to be attached to a deck or a hull of the vessel over a moon pool of the vessel. 
     
     
       6. A motion compensating system according to  claim 1 , wherein the vessel is a jack-up boat. 
     
     
       7. A motion compensating system according to  claim 1 , wherein the insert bearing sleeve and the slip bowl move angularly with the angular movement of the riser. 
     
     
       8. A motion compensating system according to  claim 1 , wherein the spherical bearing comprises an outer ring and a spherical inner ring, and the outer ring is encased between the bearing retainer and the second floor. 
     
     
       9. A method for compensating for relative motion between a vessel, a heave floor unit, and a subsea riser, the method comprising:
 attaching the heave floor unit to a deck or a hull of the vessel, the heave floor unit comprising:
 a first floor that is attached to the deck or the hull, a second floor, and a plurality of hydraulic cylinders connecting the first floor to the second floor; 
 a bearing retainer attached to the second floor; 
 a spherical bearing provided between the second floor and the bearing retainer, wherein the spherical bearing includes a central opening therethrough for the riser to allow angular movement of the riser relative to the heave floor unit; 
 an insert bearing sleeve at least partially located inside the central opening of the spherical bearing; and 
 a slip bowl attached to the insert bearing sleeve, 
 wherein each of the first floor, the second floor, the bearing retainer, the insert bearing sleeve and the slip bowl have an opening therethrough that is aligned with the central opening of the spherical bearing; 
 
 inserting the subsea riser through the central opening of the spherical bearing and the opening of the first floor, the opening of the second floor, the bearing retainer, the insert bearing sleeve and the slip bowl; and 
 actuating the plurality of hydraulic cylinders in response to motion of the vessel relative to the second floor, and in response to motion of the heave floor unit relative to the angular movement the subsea riser. 
 
     
     
       10. The method according to  claim 9 , wherein the plurality of hydraulic cylinders are actuated to keep the second floor at a constant level, and to keep the subsea riser at a constant tension. 
     
     
       11. The method according to  claim 9 , wherein the step of actuating the plurality of hydraulic cylinders comprises differentially actuating individual hydraulic cylinders within the plurality of hydraulic cylinders in response to a pitch motion, a roll motion, a yaw motion, or combinations thereof, by the vessel. 
     
     
       12. The method according to  claim 9 , wherein the heave floor unit is attached to the deck or the hull of the vessel over a moon pool of the vessel. 
     
     
       13. The method according to  claim 9 , wherein the heave floor unit is attached to a cantilever portion of the vessel.